On Fri, Mar 04, 2016 at 02:51:42PM +0800, Peng He wrote:
> Hi,
> I installed some rulesets generated by ClassBench (a ruleset benchmark
> for generating ACL and FW rules) in Open vSwitch, and I find many megaflow's
> mask has
> discontiguous bits. Like mask = 0xfc in network byte order. After some code
> investigation I find the problem is in the function *mask_set_prefix_bits*:
>
>
>
>
> staticvoidmask_set_prefix_bits(struct flow_wildcards *wc, uint8_t be32ofs,
> unsignedint n_bits)
> {
> ovs_be32 *mask = &((ovs_be32 *)&wc->masks)[be32ofs];
> unsignedint i;
>
> for (i = 0; i < n_bits / 32; i++) {
> mask[i] = OVS_BE32_MAX;
> }if (n_bits % 32) {
> mask[i] |= htonl(~0u << (32 - n_bits % 32));
> }}
> For example, if the input n_bits = 6, the mask should be 0x2f, as there is 6
> contiguous bits. However, the current code will generate 0xfc:
> (0xFFFFFFFF << (32 - 6) ) = 0xFC000000
> and htonl (0xFC000000) = 0xFC.
> I am writing this to make sure that I am correct. The OVS code I use is 2.4
> release version.
0xffffffff << (32 - 6) == 0xfc000000, which yields the bytes "fc 00 00
00" in hex, or "11111100 00000000 00000000 00000000" in binary, when
stored into memory in network byte order.
I don't see the problem.
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